I'm not sure if the information in the manual is correct, thus why I posted this thread. First of all, the markings on page 8 differ to those on page 9. Secondly, a Skywatcher rep told someone in this thread that the spacing should be 69.8mm from the metal cell. The rep went on to say that the number in the manual is from the lens element itself, but the document clearly says otherwise.

It's probable that the rep is correct, but I just wanted to hear from someone who'd successfully used the flattener to be sure that was the case before forking out a big chunk of cash on adapters.

Interesting.. I checked the Canadian Skywatcher manual, and it is the same. I have an Esprit 150, and page 8 and 9 of the manual provides two distances, 100mm from the front of the ring with the writing on it, and 96mm from the back of the ring. Have a look at this link and you will see what I mean:

I think I would try the flattener for myself and determine the correct spacing first hand before investing in a Precise Parts adapter. Your own spacing may vary from any manual spec and/or other user depending on whether you have a filter and so forth in your imaging train.

Interesting.. I checked the Canadian Skywatcher manual, and it is the same. I have an Esprit 150, and page 8 and 9 of the manual provides two distances, 100mm from the front of the ring with the writing on it, and 96mm from the back of the ring. Have a look at this link and you will see what I mean:

This suggests to me that perhaps Skywatcher updated the 150mm manual, but forgot to update the 120mm manual(or made and error).

My best advice would be to contact Skywatcher directly.

Eric

Ahh, that's very interesting. I think you might be right. I recalled a thread where a guy who'd bought an Esprit was livid after being given the wrong information by Skywatcher and then buying an expensive custom adapter from precise parts that was inappropriate. May be that they corrected the 150's but not the 120's manual.

I think I would try the flattener for myself and determine the correct spacing first hand before investing in a Precise Parts adapter. Your own spacing may vary from any manual spec and/or other user depending on whether you have a filter and so forth in your imaging train.

Good point, Adam. I'm not sure if I have appropriate spacers to check it out before buying the part though. The tricky part is the OAG, but I don't really need that in the mix, so maybe I can work something out without it.

I've seen several figures for correct spacing of this flattener. Is anyone able to confirm, based on experience, what has actually worked?

I would suggest emailing Kevin at Skywatcher to get a clarification: klegore@skywatcherusa.com

Happened to see this thread today and last night I was setting up the Esprit120 flattener with my ASI1600.

I was puzzled about the discrepancy in the manual too.

Trying to find which one is correct, I used the DSLR focal plane marking

to determine where the 75mm backfocus ends.

Since the Esprit is optimized for DSLR, using all its supplied adapters on the DSLR should guarantee the correct setup from which the 75mm distance can be measure from the focal plane marking on the DSLR body.

IMHO, I would stick to the 75mm backfocus provided by the manufacturer and not to do this by trial-and-error. The backfocus of any flattener/reducer is specifically designed to give the lowest aberration possible. Any deviation could mean the optics are working outside the design parameters. If a filter is added BETWEEN the CCD and the flattener, like in my case a 3mm thick filter, the light path is lengthened by 1/3 of that. So instead of 75mm, my setup has a backfocus distance of 76mm.

My finding is same as what the manual says, start of the male thread, the edge of the flattener.

Lee, don't forget that the filter in a filter wheel behind the flattener will affect spacing. Using the general rule of 1/3, a 3mm filter will require adding 1mm to the spacing distance from the back of the flattener. I am going through this exact exercise setting up my 152mm refractor to work with the ASI1600/QHY filter wheel combo, and my Hotech Flattener. In my case my Baader 36mm filters are 2mm thick so i need to add 0.66mm of spacing from the flattener. There is a recent thread here that discusses spacing from flatteners and examines statements made by Don from Astrodon and other experts.

After having yet more issues with this, I was searching trying to find posts by the guy who had issues and I stumbled across my own thread. Thanks so much for that detailed post, Samuel, I really appreciate it. Your logic seems sound. I've now swapped out some spacers and have it within 0.5mm of the 75mm total, assuming my calipers are reliable

Samuel, did you ever get a chance to confirm that spacing? I too am trying to use this with the ASI 1600. I should be able to confirm it myself tonight anyway.